The invention relates to a method for the open-loop or closed-loop control of the amount of water which is added to a fuel before said fuel is supplied to the high-pressure fuel pump of an internal combustion engine, and the invention also comprises a device which is suitable for carrying out said method.
Considerable technical progress is being constantly achieved in the case of internal combustion engines. The consistent increase in the specific power with a simultaneous reduction in fuel consumption and the reduction in the quantity of pollutants ejected are characteristic of this progress. The gasoline engine in particular is currently considered to be one of the most economic and most environmentally compatible thermal engines.
Modern fuel injection systems control the fuel injection time and the fuel injection quantity, for example, by using the data from the air mass flow meter, the charging pressure present and with additional consideration of the exhaust gas temperature and further measurement values. For this purpose, said engine controller electrically actuates one valve per cylinder (individual to the cylinder), namely the injector which replaces the conventional injection nozzles of classic gasoline engines.
The use of water-containing fuels constitutes a possibility in particular of equipping the gasoline engine even for future challenges (for example in respect of stricter exhaust gas legislation) since the injection of water into the fuel is a method which can contribute to achieving the aims of increasing power or reducing consumption and to lower pollutant emission.
The injection of water makes it possible, on the basis of the evaporation enthalpy which is high in comparison to gasoline, to reduce the temperature of the fresh gas prior to the combustion and therefore to shift the knock limit to earlier center of gravity positions and to reduce the full load consumption or raise the compression ratio in order to optimize the partial load consumption.
Since gasoline fuel and water are difficult to mix, there are various methods in the prior art for producing an emulsion for motor vehicle engines. Firstly, there are methods for providing fuel-water emulsions in advance. For this purpose, the water can be mixed with a small quantity of fuel, and the mixture conveyed during operation simultaneously with the main quantity of fuel to the injection nozzle and injected into the combustion chamber. Alternatively, a stable microemulsion can be produced by adding surfactants. Furthermore, an addition of methanol into the fuel may be advantageous.
Secondly, the emulsion may be produced only when required, i.e. on-board in the vehicle, and the application is based on such an “on-board” mixed emulsion. This emulsion has the advantage over the pre-mixed emulsions that the water content of the fuel can be adjusted as needed during the engine operation, and the currently required quantity and composition of the water-fuel emulsion can then be supplied to the high-pressure fuel pump or to the common rail injection system.
The mixing of fuel with water can furthermore also take place directly at the injector since the closer the mixing site is located to the combustion chamber, the smaller is the period of time between emulsion generation and preparation and therefore the “dead time.”
For the injection of water, use is made in the prior art of a water pump with which the quantity of water to be added to the fuel can be conveyed as needed.
It is the object of the invention to provide a method which is simple to realize and a simply constructed device for the open-loop or closed-loop control of the amount of water added to the fuel.
The invention achieves the object in a first aspect by a method for the open-loop or closed-loop control of the amount of water which is added to a fuel before said fuel is supplied to the quantity control valve of the high-pressure fuel pump of an internal combustion engine. This method comprises splitting the fuel supply to the high-pressure fuel pump into a first branch with a Venturi tube in the fuel path downstream of the fuel pre-feed pump (electric fuel pump), which has a negative pressure connection, and into a second branch with a stop valve. Water is supplied to the negative pressure connection of the Venturi tube via a water supply line. The amount of water sucked up by the Venturi tube is controlled by open-loop or closed-loop control by the fact that, in order to increase the amount of water in the first branch, the fuel flow in the second branch is reduced by closing the stop valve (which also includes an incomplete closing), and that, in order to reduce the amount of water in the first branch, the fuel flow in the second branch is increased by opening the stop valve (which also includes partial or further opening). The fuel in the second branch and the fuel-water mixture in the first branch are then conveyed to the quantity control valve of the high-pressure fuel pump.
A second aspect of the invention is a device for adding an open-loop-controlled or closed-loop-controlled amount of water into the fuel supply of an internal combustion engine, which comprises a high-pressure fuel pump with a quantity control valve. The device has a fuel supply line which leads to the quantity control valve and divides into a first branch and a second branch. A Venturi tube which has a negative pressure connection is provided in the first branch, and there is an adjustable stop valve in the second branch. Furthermore, a water supply line is provided which is connected to the negative pressure connection of the Venturi tube, and also connections of the first and second branch of the fuel supply line to the quantity control valve of the high-pressure fuel pump.
With the invention, the water pump, which is provided in the prior art, in the fuel supply section is saved. It is replaced by a Venturi tube which does not have any mechanically movable parts, and by a stop valve, for which there are readily suitable and in particular robust embodiments in the prior art. This considerably reduces the complexity of the water injection system.
Further advantages are afforded by embodiments of the claimed method and of the claimed device.
In comparison to a continuous closed-loop control of the stop valve, a keyed closed-loop control at a sufficiently high frequency is particularly simple and robust.
If the water-fuel mixture in the first branch and the fuel in the second branch are guided to the quantity control valve of the high-pressure fuel pump via separate supply lines, the small dead volumes mean that the system is capable of reacting particularly rapidly to changing requirements.
A shut-off valve for the complete (or partial) shutting off of the first branch with the Venturi tube permits a rapid transition between operation with and without injection of water.
The method according to the invention and the device according to the invention are used in particular in the case of gasoline fuel.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawing.